The cementiferous compositions with which this invention is concerned include concretes which comprise cement, coarse and fine aggregates and water; cement pastes which comprise cement and water, and mortars which comprise cement, sand and water; lime, sand and water, or mixtures containing both lime and cement. The invention is also applicable to high-pressure, steam-cured concretes comprising cement, aggregate and water; lime or limestone and siliceous materials such as silica flour and water.
The additives with which this invention is concerned are sometimes referred to as plasticizers and/or superplasticizers for concrete. Their purpose is to improve the flow characteristics of the cementiferous compositions containing them so that they may be pumped or effectively poured to fill all the spaces in a mould or other structure and yet not have their strength characteristics weakened by the inclusion of excessive amounts of air which, in certain circumstances, would be undesirable. In addition, these additives can be used to design cementiferous compositions with a reduced water content. This permits the production of concretes having higher compressive strength when cured and also adequate flow properties for certain applictions.
Various additives for use in cementiferous compositions have been previously proposed, including for example, lignosulphonates and sodium naphthalene sulphonate formaldehyde condensates. Details of such materials are set out in "Chemical Admixtures for Concrete" by M. R. Rixom, published by E. and F. N. Spon Limited, London, and by the Halstead Press, a division of John Wiley and Sons Incorporated of New York, U.S.A., where at page 34, various known additives are considered.
Various polymeric materials have been evaluated as plasticiser additives for cementiferous compositions and it has been found that certain polymers and their soluble salts comprising polymerisable carboxylic acids and the hydroxyalkyl esters of such acids have a definite utility in this application. Such polymers are described in U.S. Pat. No. 4,473,406 (European Patent specification 0097513).